1. Field of the Invention
Embodiments of the invention generally relate to electronics. In particular, embodiments of the invention relate to analog integrated circuits.
2. Description of the Related Art
Analog amplifiers are widely use in electronic devices. Applications include, but are not limited to: buffers, attenuators, gain amplifiers, current amplifiers, filters, drivers, interface circuits between digital and analog domains, and the like. One type of amplifier is known as an operational transconductance amplifier (OTA). An OTA receives a differential input voltage and generates an output current. OTAs are commonly used in, for example, variable frequency oscillators, filters, variable gain amplifiers, and the like.
It is desirable for an analog amplifier to have relatively good performance, to be inexpensive to manufacture, to be usable in a wide range of power supply voltages, to be able to swing relatively large output voltages, and the like. For example, in a mobile battery-powered application with a relatively low-voltage power supply, analog amplifiers preferably efficiently utilize the available supply voltage.
In the context of a switched-capacitor filter, an operational transconductance amplifier (OTA) is described by Rinaldo Castello, et al., in “A 500-nA Sixth-Order Bandpass SC Filter,” IEEE JOURNAL OF SOLID-STATE CIRCUITS, Vol. 25, No. 3, June 1990, pp. 669-676. However, the application of the foregoing amplifier appears to be prone to relatively severe mismatches for the drain-to-source voltages of the mirror transistors. For example, with reference to Castello, ibid, the drain-to-source voltages for the following three current mirrors: M7/M9, M8/M11 and M13/M15 all appear to be mismatched.